Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$158.95	8.398%	$172.2986	$172.30	$172.30	$172.30
Purchase #2	$67.55	6.223%	$71.7536	$71.75	$71.75	$71.80
Purchase #3	$16.97	11.371%	$18.8997	$18.90	$18.90	$18.90
Purchase #4	$75.34	10.552%	$83.2899	$83.29	$83.30	$83.30
Purchase #5	$63.84	11.544%	$71.2097	$71.21	$71.20	$71.20
Purchase #6	$88.79	5.398%	$93.5829	$93.58	$93.60	$93.60
Purchase #7	$243.29	13.157%	$275.2997	$275.30	$275.30	$275.30
7 purchase totals =	$714.73		$786.3341	$786.33	$786.35	$786.40